1. Field of the Invention
This invention relates to an electromagnetic shielding filter composed of a plastic or glass board and attached at the front of a display device and, in particular, to an electromagnetic shielding filter suitably adapted for a plasma display panel (PDP) TV. Also, this invention can be adapted for a field emission display (FED) or cathode-ray tube (CRT) monitor.
2. Description of the Related Art
Display devices such as PDP, CRT and FED emit unnecessary electromagnetic waves which may cause a malfunction or noise in peripheral devices or be harmful to humans. Therefore, they need to be equipped with some electromagnetic shielding filter to eliminate the electromagnetic waves. General electrical devices can be electromagnetic-shielded by disposing a conductor around them. However, in case of the display devices, the electromagnetic shielding filter needs to be transparent as well as being conductive.
JP-A-2000-174488 discloses an electromagnetic shielding transparent window material that is composed of two transparent boards and a conductive mesh formed of a metal covered conductive fiber and disposed between the boards, where the mesh is integrated with the boards by an adhesive resin.
The transparent board of the electromagnetic shielding transparent window material are generally made of plastic or glass. The plastic or glass board has a serious defect in aspect of the mechanical strength that it may cause a crack when a strong load is externally applied thereto. Thus, the transparent board needs to have a breaking strength property against the external force to protect the panel from the external force.
In order to compensate the mechanical strength of the electromagnetic shielding transparent window material, JP-A-2000-174488 teaches using a special chemical reinforced glass for at least one of the two transparent boards. However, in this approach, the production cost must be increased since the special chemical reinforced glass is used instead of the commercially-available plastic film.
On the other hand, the electromagnetic shielding filter needs to be lightweight as well as the mechanical strength above a certain level since it is attached at the front of the display panel. In order to make the filter lightweight, it is proposed to reduce the thickness of the transparent board. However, in this way, the strength of the whole electromagnetic shielding filter cannot be secured. In general, the mechanical strength is incompatible with the weight saving. Thus far, the incompatible properties are difficult to satisfy together in the conventional display front filter board.
JP-A-2001-22283 discloses an electromagnetic shielding filter having transparency and conductivity, which is produced such that a conductive metal is deposited on a transparent board and a mesh wiring is then formed by etching it, or a mesh structure is formed by arranging wires in the length and width directions. However, in case of forming the mesh wiring by etching, the production cost will be increased and the transparency (wire invisibility) thereof is too low to meet the market needs.
In case of forming the mesh structure by arranging wires in the length and width directions, the diameter of a wire available is as large as about 30 to 40 μm and, therefore, must be further reduced to satisfy the transparency (wire invisibility). In case of wires, the normal wire drawing process needs to conduct the annealing several times during the operation and it is difficult to produce a ultrafine wire as thin as 20 μm φ from a normal copper or copper alloy material. Thus, it is desired that a wire material for the electromagnetic shielding filter has such a ultrafine-wire processability that does not cause a breaking even in tough area reduction processing so as to produce the ultrafine wire with a diameter of 20 μm φ or less.